While elected officials in Washington feud this week about how best to curb spending to avert the "fiscal cliff," international delegates at the U.N. climate talks instead say the United States is too tightfisted when it comes to helping poorer nations weather the effects of man-made climate change.

As with other aspects of the negotiations, President Obama comes in for a hefty share of the blame.

His negotiators have been too cautious, say participants and observers of the climate gathering. They have not done enough to reassure other countries that the United States will maintain its levels of international climate aid, now that the initial period of fast-start financing is drawing to a close with no new firm agreement on funding expected until at least 2015.

Nor has the leader of the world's largest economy said how much it will contribute to the $100 billion a year by 2020 that developed countries pledged at Copenhagen, Denmark, three years ago, even though the United States took the lead on that commitment at the time.

Top U.S. negotiator Todd Stern yesterday said during a press briefing that the United States would hold steady on climate financing and eventually increase its level of support for adaptation and mitigation efforts in poor countries. The nation estimates it has contributed $7.5 billion in total to fast-start financing in the past three years.

"We have every intention to continue pushing forward with funding of that same kind of level to the greatest extent that we can," he said, noting that Congress is responsible for appropriations and that these are "tough fiscal times."

He added that the United States remains "committed to the longer-term goal of mobilizing funding by 2020 in the context of the right kind of mitigation and transparency."

But that wasn't enough for advocates and representatives from poor countries, who said Stern and his deputy Jonathan Pershing should adopt a more aggressive tone and offer more specifics about what the United States plans to put on the table in terms of climate finance.

David Waskow of Oxfam America said the administration should not cite gridlock in Washington as a reason to shirk the president's responsibility to lead.

"We saw with Copenhagen, in fact, that the president got out ahead of Congress and pushed Congress along," he said. "That's the role he needs to play. It's not simply one of being trapped by congressional realities, but one that he can in fact shape."

While the public sector will have to contribute a hefty share of the overall U.S. funds for climate aid, Waskow suggested that not all those funds may need to be appropriated. Some could come from dedicated sources like a future price on aviation or shipping emissions.

U.S. lawmakers have sometimes dismissed foreign aid as a budget item the country cannot afford as it struggles to come back from economic recession. But Samantha Smith of the World Wildlife Fund said Obama should communicate a different narrative: that helping other nations reduce their emissions is self-preservation for an America increasingly vulnerable to the effects of climate change.

"Climate finance as it goes to Congress has to be reframed in the sense that you're not doing anyone a favor," she said. "You're doing yourself a favor, and you're also paying for some of your responsibility for your own emissions."

But it seems unlikely that Republicans in Congress will see it that way. Sen. David Vitter (R-La.) told Greenwire in an email today that Stern's statement that the United States would continue to fund climate aid at current levels was troubling.

The incoming top Republican on the Senate Environment and Public Works Committee has introduced a resolution rejecting a carbon tax. He also has asked the Treasury Department to release internal correspondence he says might show it is making a closed-door bid to enact a carbon tax in the second Obama term despite administration statements to the contrary.

"This is exactly why we need to find out what the Treasury Department is saying about a carbon tax, and if that is how they intend to pay for these international programs," he said in the email. "Administration officials are overseas promising large sums of money, meanwhile the United States is in a financial mess."

But Waskow said that even if many in Congress oppose climate finance, Obama can still make headway by making a bold commitment. He can then put the administration's weight behind that commitment by putting it in writing as part of the U.N. process and reflecting it in budget requests and public statements.

"What the president puts in a budget request has significant import for the way that Congress goes about legislating appropriations," he said, noting that the Democratic-controlled Senate would be swayed by Obama's priorities.

He noted that the United Kingdom today committed to increase its fast-start funding levels by half in the coming years, the first such pledge by any developed country. Such a commitment should spur other countries to act, he said, especially the United States.

But Andrew Light, an international climate change expert with the Center for American Progress, said it was unfair to compare what Obama can do in the United States, given its current political realities, to what the United Kingdom can pledge.

A parliamentary system like Great Britain's doesn't have to go through negotiations between an executive and legislative branch to approve a budget, he noted.

"We can't wish away the constitutional separation of powers overnight for the fiscal cliff we now face, so certainly not for climate appropriations either," he said.

But delegates from other countries have expressed frustration with appeals by the United States for them to understand Washington's woes.

"We understand that there are internal domestic economic problems," said Farah Kabir of ActionAid Bangladesh. But she said the United States had not been ambitious even before the current recession. "It's very difficult to explain to a country like mine where we are on the front line of all kinds of climatic changes that is not going through an economic recession, and we can't make any changes."